Cutting tools of the type that makes use of a basic body, as well as a separate, replaceable cutting part, may in practice comprise drilling tools, milling tools, such as end mills or slitting cutters, thread cutters, etc. Usually, the basic body consists of an elongate shaft of a cylindrical basic shape. In modern machine tools, the basic bodies are so sophisticated and expensive that they, for economical reasons, cannot be integrated with the cutting part, which constitutes the wear part of the tool and has a limited service life. In other words, it is profitable to make the actual cutting part in the form of a separate, releasable unit, which by those skilled in the art usually is denominated “loose top”, and which can be exchanged after wear, while the expensive basic body can be used for a longer time (usually 10 to 20 exchanges). In practice, the loose top is manufactured entirely or partly from a hard, wear-resistant material, such as cemented carbide or the like, while the basic body is made from a material having greater elasticity, e.g., steel. It should also be pointed out that tools of the kind in question primarily—though not necessarily—are intended for the machining of workpieces of metal.
The development of loose top tools is particularly intense and interesting in the field of drilling. For drilling purposes, either simple drilling machines or multioperation machines are used, which in both cases include a strong and rigidly mounted machine spindle or holder, in which a rear end of the basic body of the cutting tool can be fixed, at the same time as the front end of the basic body is freely available for the mounting and dismounting of the loose tops that should carry out the cutting or chip removing task in the workpieces in question. Under absolutely ideal conditions, not only the geometrical center axis of the basic body, but also the geometrical center axis of the loose top should coincide exactly with the geometrical center axis of the machine spindle, in order to generate a hole having optimum precision in respect of shape as well as position in the workpiece. However, in practice it is difficult to reach an optimum precision, above all because of inevitable tolerances in the interface between the loose top and the basic body, which, as known, are individually manufactured in different operations and from different materials, but also because of various form defects in the basic body as well as the loose top. Therefore, in reality the result will not infrequently be that the drill wobbles when entering a workpiece, i.e., the tip of the loose top is unintentionally located offset from the geometrical center axis of the machine spindle, which determines the geometrical position of the hole to be made. Instead of moving linearly into the workpiece, the tip of the loose top, therefore, initially describes a circling or planetary motion before being stabilized in a linear track of motion that may be located more or less far from the intended track of motion.